Sensor sizes and f stops

Started 7 months ago | Discussions
starlight110
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Sensor sizes and f stops
7 months ago

Hi, I know that in digital cameras, the bigger the sensor size the less noise and thus better light sensitivity, but I wonder if there´s a way to directly correlate sensor size and fstop, like doubling the sensor size from 1/1,8 to 1/3,6 would correlate to one fstop. I have an old low end A630 camera which has a 1/1,8 sensor size and performs average in low light, I want to buy a new more expensive camera but nowadays they make them all with 1/2,3 sensors and it would be weird to spend more money to buy a camera which performs (only from the sensor size factor) worse in low light. Would 1/1,8 to 1/2,3 size woiuld be much difference?

Thanks for the answers

trekkeruss
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Re: Sensor sizes and f stops
In reply to starlight110, 7 months ago

There are compact cameras that have sensors bigger than 1/2.3"; lots of them, in fact. The most conspicuous are the Sony RX100 and RX100 mkII, which have 1" sensors. Then there is a whole crop of 1/1.7" cameras from Canon, Fujifilm, Nikon, Panasonic, Olympus. If you don't require a zoom lens, there are even compacts that have DSLR-size sensors. How large a sensor you can get depends only on how much money you are willing to pay.

Keep in mind that a wide aperture lens is still desirable, regardless of sensor size.

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OpticsEngineer
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Re: Sensor sizes and f stops
In reply to starlight110, 7 months ago

There are many camera similar in zoom range and basically the same chip size as your A630 but with much improved high ISO / low light performance due to better sensors and also faster lenses.

One place to look is the link below.

http://www.dpreview.com/articles/2367736880/roundup-enthusiast-zoom-compact-cameras

 OpticsEngineer's gear list:OpticsEngineer's gear list
Olympus XZ-1 Canon PowerShot SX40 HS Canon PowerShot SX260 HS Sony Cyber-shot DSC-HX20V Fujifilm XF1 +19 more
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darklamp
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f-numbers are independent of sensor size
In reply to starlight110, 7 months ago

I wonder if there´s a way to directly correlate sensor size and fstop

The way exposure system values work is that they are designed to give the same exposure on different systems, regardless of sensor size ( or film size ).

So there is no correlation between sensor size and f-number.

What is sometimes done is to calculate an equivalent f-number for a system to relate it to another. This is normally based on depth of field formula. However this ONLY relates to depth of field. You can also calculate the absolute size of the aperture from the f-number and the sensor size and compare them that way.

While there are small differences from system to system, using the same ISO, shutter speed and aperture (f-number) will result in the same exposure.

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wyldberi
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Re: Sensor sizes and f stops
In reply to starlight110, 7 months ago

According to information here on dpreview, the Canon A630 was first introduced about 7 years ago. Since that time camera manufacturers have made significant improvements in performance.

Perhaps giving us some idea of the price range you're willing to spend on your new camera would help us come up with a few suggestions. Also, what kinds of pictures do you take, and can you be more specific about the kinds of shortcomings your current camera has that you'd like to have improved upon.

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starlight110
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Re: Sensor sizes and f stops
In reply to wyldberi, 7 months ago

Thanks for the answers!

In digitalcameras there´s a great deal of tradeoffs between sensor size, optics and Price. I want to buy a superszoom with a mínimum of 12x to about 420mm eqiv and will use it a lot for videos, in fact, the only reason why I´m considering a digicam instead of a camcorder is the sensor size. After searching I found that the cameras with the proper optics and price usually have 1/2,3´sensors, for instance canon sx510 with 720mm, f/5,8 tele and a smaller but newer sensor. To compare it to my old A630 I wanted to know if the smaller sensor size has a big influence or not, my A630 has f/4,1 tele and the bigger sensor, the sx510 has f/5,8 tele (a whole fstop slower) and the smaller sensor, would in this case be a great difference when using both cameras in tele?

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wyldberi
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Re: Sensor sizes and f stops
In reply to starlight110, 7 months ago

starlight110 wrote:

Thanks for the answers!

In digitalcameras there´s a great deal of tradeoffs between sensor size, optics and Price. I want to buy a superszoom with a mínimum of 12x to about 420mm eqiv and will use it a lot for videos, in fact, the only reason why I´m considering a digicam instead of a camcorder is the sensor size. After searching I found that the cameras with the proper optics and price usually have 1/2,3´sensors, for instance canon sx510 with 720mm, f/5,8 tele and a smaller but newer sensor. To compare it to my old A630 I wanted to know if the smaller sensor size has a big influence or not, my A630 has f/4,1 tele and the bigger sensor, the sx510 has f/5,8 tele (a whole fstop slower) and the smaller sensor, would in this case be a great difference when using both cameras in tele?

Unfortunately, I'm having a difficult time following you. The f-stop measurement of a lens refers to the size of the lens aperture; this controls how much light the lens captures. The higher the number, the smaller the hole, and the less light you have being captured. Less light means you will have a poorer image quality being recorded. The image will be less sharp, and contain less detail.

The f-stop has nothing to do with the sensor.

Also, I don't think it's possible to equate image quality produced by a still camera with a given sensor size to a video camera with the same size sensor. They are two different systems. Video cameras used in television studios to produce live or taped broadcasts use sensors that are smaller than the sensors used in digital cameras.

In still image cameras, the only real advantage a 24mm x 36mm sensor has over a sensor measuring 16mm x 24mm is when it comes time to print the pictures each captures in enlargements measuring 2 meters x 3 meters. That's where the noise shows up. Print the same images at 24cm x 36cm and you won't be able to tell the two pictures apart.

The bottom line is, if you want to capture real time moving objects moving around you, get a video camera. If you want to take still pictures, get a camera that's built for that purpose. Don't handicap yourself by buying the wrong tool and trying to force it to do what you thought it would.

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darklamp
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Re: Sensor sizes and f stops
In reply to starlight110, 7 months ago

In digitalcameras there´s a great deal of tradeoffs between sensor size, optics and Price.

OK

I want to buy a superszoom with a mínimum of 12x to about 420mm eqiv

Well that limits you very quickly to a sensor size that's small or a camera that's relatively large.

A DSLR like a D3200 with an 18-200 covers about 12x and equates to about 300m in full frame terms.

and will use it a lot for videos, in fact, the only reason why I´m considering a digicam instead of a camcorder is the sensor size.

Why is sensor size an issue for you ?

After searching I found that the cameras with the proper optics and price usually have 1/2,3´sensors, for instance canon sx510 with 720mm, f/5,8 tele and a smaller but newer sensor. To compare it to my old A630 I wanted to know if the smaller sensor size has a big influence or not, my A630 has f/4,1 tele and the bigger sensor, the sx510 has f/5,8 tele (a whole fstop slower) and the smaller sensor, would in this case be a great difference when using both cameras in tele?

Exposure settings are going to produce about the result in terms of what for simplicity we'll call brightness. That's the idea of these numbers consistent exposure across formats.

Modern sensors have improved, but there are more factors to consider. In practical terms the differences would be minor, IMO, for normal print and display sizes.

If you want a significant different you need larger sensor. Maybe a 4/3 system or an NEX. Panasonic make some nice systems and a twin lens kit with a Panasonic G3 ( used or new ) would be a good choice.

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Tom Axford
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Re: Sensor sizes and f stops
In reply to starlight110, 7 months ago

starlight110 wrote:

Thanks for the answers!

In digitalcameras there´s a great deal of tradeoffs between sensor size, optics and Price. I want to buy a superszoom with a mínimum of 12x to about 420mm eqiv and will use it a lot for videos, in fact, the only reason why I´m considering a digicam instead of a camcorder is the sensor size. After searching I found that the cameras with the proper optics and price usually have 1/2,3´sensors, for instance canon sx510 with 720mm, f/5,8 tele and a smaller but newer sensor. To compare it to my old A630 I wanted to know if the smaller sensor size has a big influence or not, my A630 has f/4,1 tele and the bigger sensor, the sx510 has f/5,8 tele (a whole fstop slower) and the smaller sensor, would in this case be a great difference when using both cameras in tele?

Unfortunately, the camera manufacturers are not particularly helpful when trying to make comparisons between different cameras.

Sensor sizes get quoted by manufacturers in a variety of different ways:

  • DSLRs are generally specified as FF or APS-C
  • Sometimes sensors are quoted as 4/3", 1", 1/1.7", 1/2.3", etc.
  • Sometimes sensors are quoted as something like 8mm x 6mm
  • Sometimes the crop factor is given

Most photographers are not able to instantly convert between these various different measures of the same thing (sensor size).

I prefer to use the crop factor relative to FF. To work this out for a sensor specified as 1/2.3", you simply need to know that FF corresponds to 8/3" = 2.7" on this scale. So the crop factor for the 1/2.3" camera is 2.7 x 2.3 = 6.2.

You can use the crop factor to work out the equivalent lens (with respect to field of view, depth of field, background blur, diffraction effects) by simply dividing the focal length and the f-number by the crop factor.

So a 50mm f/11 lens on FF is equivalent to a 8.1mm f/1.8 lens on a camera with a 1/2.3" sensor (with respect to field of view, depth of field, background blur, diffraction effects).

[Of course, the exposure is still determined by the actual f-number, you do not multiply by the crop factor.]

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Christof21
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Re: f-numbers are independent of sensor size
In reply to darklamp, 7 months ago

darklamp wrote:

I wonder if there´s a way to directly correlate sensor size and fstop

The way exposure system values work is that they are designed to give the same exposure on different systems, regardless of sensor size ( or film size ).

So there is no correlation between sensor size and f-number.

What is sometimes done is to calculate an equivalent f-number for a system to relate it to another. This is normally based on depth of field formula. However this ONLY relates to depth of field. You can also calculate the absolute size of the aperture from the f-number and the sensor size and compare them that way.

While there are small differences from system to system, using the same ISO, shutter speed and aperture (f-number) will result in the same exposure.

Well, not really...

There is a correlation between sensor size and f-number. You can calculate an equivalent f number by multiplying by the crop factor. And it works for dof (same resulting dof) AND for the "light" ( same quantity of noise in the resulting image). You just have to stop down with the larger sensor and to raise the ISO to compensate.

The following link may help:

http://www.josephjamesphotography.com/equivalence/

Inthink this is the most misunderstood concept in photography....

So F1.8 with a P&S is like having F10 with a FF . See the difference ???

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darklamp
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No correlation
In reply to Christof21, 7 months ago

There is a correlation between sensor size and f-number.

No there isn't.

f-numbers are defined precisely to remove any correlation between aperture size ( i.e. the absolute measurement ) and the sensor.

You can calculate an equivalent f number by multiplying by the crop factor.

That's not a correlation.

http://en.wikipedia.org/wiki/Correlation_and_dependence

That's you defining another value using two others. Your new value has a dependence on sensor size, but the f-number you start from does not.

As I've already explained, that kind of equivalence is limited to depth of field.

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Christof21
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Re: No correlation
In reply to darklamp, 7 months ago

darklamp wrote:

There is a correlation between sensor size and f-number.

No there isn't.

f-numbers are defined precisely to remove any correlation between aperture size ( i.e. the absolute measurement ) and the sensor.

You can calculate an equivalent f number by multiplying by the crop factor.

That's not a correlation.

http://en.wikipedia.org/wiki/Correlation_and_dependence

That's you defining another value using two others. Your new value has a dependence on sensor size, but the f-number you start from does not.

As I've already explained, that kind of equivalence is limited to depth of field.

I answer to the op who wonders what really means a f number when comparing with different sensor size.

Different sensor size should be taken into account, of course ! And you can calculate an "equivalent" aperture taking into account the crop factor.

There is a relation which "correlates" these equivalent apertures, I really think this is what the op wants to know.

It is very important to be aware of this. The op could buy a f1.8 with a1/2.3" thinking that it is better that a f2.8 with a 1" sensor. The 1" sensor is better for dof AND low light conditions.

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darklamp
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Re: No correlation
In reply to Christof21, 7 months ago

I'm not sure if English is your first language, but "correlate" does not mean what you're saying it does.

If there was a correlation between f-number and aperture you could find the one from the other, assuming other factors were constant.

You cannot.

You are just defining a value and as you factor in sensor size that defined value has a correlation with sensor size.

But the original f-number has NONE.

And if you start using the so-called equivalent f-number you have defined, you cannot use it for exposure calculations. So they are not equivalent in real exposures as you would have to use different shutter speeds and/or ISO values for different sensor sizes to get the same exposure.

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starlight110
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Re: No correlation
In reply to darklamp, 7 months ago

Christof21 wrote:

It is very important to be aware of this. The op could buy a f1.8 with a1/2.3" thinking that it is better that a f2.8 with a 1" sensor. The 1" sensor is better for dof AND low light conditions.

That´s about what I ment with my original question, sorry if I didn´t express it correctly since my english is not the best and I´m newbie in photography.

I will put a simple example. Let´s say I want to compare two ideal cameras. Both have ideally fully manual controls and have the same lenses. One has a 1/2,3´sensor and the other 1/1,15´,, double in size, same megapixels and of the same type. I take a picture with the two cameras in the same light situation and setting in both iso100 and 1/30 sec exposure. The cameras have exactly the same algorithms to determine the aperture so that the amount of noise is about the same, in this case would there be a difference in aperture?? if yes, how much in terms of fstops??

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starlight110
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Re: Sensor sizes and f stops
In reply to wyldberi, 7 months ago

wyldberi wrote:

Unfortunately, I'm having a difficult time following you. The f-stop measurement of a lens refers to the size of the lens aperture; this controls how much light the lens captures. The higher the number, the smaller the hole, and the less light you have being captured. Less light means you will have a poorer image quality being recorded. The image will be less sharp, and contain less detail.

The f-stop has nothing to do with the sensor.

Also, I don't think it's possible to equate image quality produced by a still camera with a given sensor size to a video camera with the same size sensor. They are two different systems. Video cameras used in television studios to produce live or taped broadcasts use sensors that are smaller than the sensors used in digital cameras.

In still image cameras, the only real advantage a 24mm x 36mm sensor has over a sensor measuring 16mm x 24mm is when it comes time to print the pictures each captures in enlargements measuring 2 meters x 3 meters. That's where the noise shows up. Print the same images at 24cm x 36cm and you won't be able to tell the two pictures apart.

The bottom line is, if you want to capture real time moving objects moving around you, get a video camera. If you want to take still pictures, get a camera that's built for that purpose. Don't handicap yourself by buying the wrong tool and trying to force it to do what you thought it would.

Thanks for clarifyng a bit, I´m a newbie in photography, I have the idea, a bigger sensor means better image and video quality and maybe better light sensitivity (of course for this, other factors like the lense is decisive) , I might be completly wrong in comparing digicams and camcorder videos but viewing videos full HD in YouTube I came to the conclusión that digicams with bigger sensors like 1/2,3´produce better looking and more detailed videos than digicams with 1/5,8´ sensors. But of course it could be only my impression only

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starlight110
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Re: Sensor sizes and f stops
In reply to darklamp, 7 months ago

darklamp wrote:

and will use it a lot for videos, in fact, the only reason why I´m considering a digicam instead of a camcorder is the sensor size.

Why is sensor size an issue for you ?

As I said above, I have the, maybe wrong Idea of comparing sensor sizes and video quality between digicams and camcorders and after looking videos in YouTube I think the larger sensors of the digicams tend to produce better quality videos than the camcorders which have smaller sensors but of course it´s just my opinión and I´m far from being an expert in this

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trekkeruss
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Re: No correlation
In reply to starlight110, 7 months ago

If both cameras have the same shutter speed and ISO settings, the aperture should be the same as well; it does not matter what size is the sensor.

FWIW, if you are primarily interested in video, a video camera is often still a better choice. Video cameras usually have much wider aperture lenses than still cameras. They are also more ergonomic for shooting video.

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Christof21
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Re: No correlation
In reply to starlight110, 7 months ago

starlight110 wrote:

Christof21 wrote:

It is very important to be aware of this. The op could buy a f1.8 with a1/2.3" thinking that it is better that a f2.8 with a 1" sensor. The 1" sensor is better for dof AND low light conditions.

That´s about what I ment with my original question, sorry if I didn´t express it correctly since my english is not the best and I´m newbie in photography.

I will put a simple example. Let´s say I want to compare two ideal cameras. Both have ideally fully manual controls and have the same lenses. One has a 1/2,3´sensor and the other 1/1,15´,, double in size, same megapixels and of the same type. I take a picture with the two cameras in the same light situation and setting in both iso100 and 1/30 sec exposure. The cameras have exactly the same algorithms to determine the aperture so that the amount of noise is about the same, in this case would there be a difference in aperture?? if yes, how much in terms of fstops??

No difference in aperture because the exposure rules are the same (triangle of exposure) whatever the sensor size is.

BUT you will have less noise with the larger sensor ! This is what is important. The difference is in fact 2 stops in favor of the larger sensor.

You could say that the larger sensor is the winner. Not that simple. In your example, you omit to say that when you take the same picture (same framing=same angle of view) , you will have less dof... So having this advantage of 2 stops is not free, you will have less dof.. If you stop down the larger sensor, you will have a similar picture in fact. With the  larger sensor, you have more choice in fact: you can get a similar picture or decide to have a shallower dof and more light. You do not have this choice with small sensors, it would need lenses with very low f number which do not exist.

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starlight110
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Re: Sensor sizes and f stops
In reply to Tom Axford, 7 months ago

Tom Axford wrote:

I prefer to use the crop factor relative to FF. To work this out for a sensor specified as 1/2.3", you simply need to know that FF corresponds to 8/3" = 2.7" on this scale. So the crop factor for the 1/2.3" camera is 2.7 x 2.3 = 6.2.

You can use the crop factor to work out the equivalent lens (with respect to field of view, depth of field, background blur, diffraction effects) by simply dividing the focal length and the f-number by the crop factor.

So a 50mm f/11 lens on FF is equivalent to a 8.1mm f/1.8 lens on a camera with a 1/2.3" sensor (with respect to field of view, depth of field, background blur, diffraction effects).

[Of course, the exposure is still determined by the actual f-number, you do not multiply by the crop factor.]

Interesting formula, that means a smaller sensor will always produce more depth of field at a given aperture?, let´s say a 1/5,8 sensor in a camcorder at f3,4 will have more depth of field than a 1/2,3 sensor at f/5,6?? sorry if comparing digicam and camcorder is wrong but I guess the optics and system would be in some aspects be similar

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olliess
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Re: Sensor sizes and f stops
In reply to starlight110, 7 months ago

starlight110 wrote:

Tom Axford wrote:

I prefer to use the crop factor relative to FF. To work this out for a sensor specified as 1/2.3", you simply need to know that FF corresponds to 8/3" = 2.7" on this scale. So the crop factor for the 1/2.3" camera is 2.7 x 2.3 = 6.2.

You can use the crop factor to work out the equivalent lens (with respect to field of view, depth of field, background blur, diffraction effects) by simply dividing the focal length and the f-number by the crop factor.

So a 50mm f/11 lens on FF is equivalent to a 8.1mm f/1.8 lens on a camera with a 1/2.3" sensor (with respect to field of view, depth of field, background blur, diffraction effects).

[Of course, the exposure is still determined by the actual f-number, you do not multiply by the crop factor.]

Interesting formula, that means a smaller sensor will always produce more depth of field at a given aperture?, let´s say a 1/5,8 sensor in a camcorder at f3,4 will have more depth of field than a 1/2,3 sensor at f/5,6?? sorry if comparing digicam and camcorder is wrong but I guess the optics and system would be in some aspects be similar

What the formula tells you is that the 6.2x crop camera will have more depth of field than the 1x crop camera whenever you use the equivalent focal length (50mm FF vs. 8.1mm on the 1/2.3" sensor) and the exact same f-number (e.g., f/11). If you use those lenses with the "equivalent" apertures of f/11 on the FF sensor and f/1.8 on the 1/2.3" sensor, the DOF will be exactly the same.

You have to keep in mind is that people usually talk about the aperture in terms of "f-number," which is the focal length divided by the (effective) aperture diameter. When you use a smaller sensor to take the same picture, it's assumed that you'll also use a shorter focal length. What this means is that the aperture diameter will actually be smaller for a given f-number. As it turns out, the depth of field will be the same between a larger and smaller sensor for the same aperture diameter! (But nobody ever sets their camera according to aperture diameter).

By the way, to get full "equivalence" between pictures taken on two different sensors, what you do is set the same shutter speed, "equivalent" apertures, and raise the ISO on the larger sensor by the appropriate number of stops. This is useful for understanding relative sensor performance, but probably not so useful for everyday use.

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